The present invention relates to a recording medium having a multilayer structure in which optically recordable and reproducible information layers are laminated, and to a recording/reproducing method and a manufacturing method for the same.
Conventionally, optical disks or optical cards are known as optical information recording media on which information can be recorded or reproduced optically. These recording media use a semiconductor laser as a light source, and a great deal of information can be recorded or reproduced by irradiating the recording media with light that is finely focused by a lens.
At present, there is much research on the above recording media to improve their recording capacities. For example, a recording medium having a multilayer structure, where recording capacity is doubled by laminating information layers for recording or reproducing information signals, has been proposed (U.S. Pat. No. 5,726,969). Under such circumstances, read-only DVD-ROM disks including two information layers have been put into practical use.
On the other hand, optical disks that can be recorded in the user""s environment have been achieved using a phase changeable material, a magneto-optical recording material, a dye material, or the like. There are two systems for recording signals on such optical disks: a sector-structure system and a continuous recording system. The former is used mainly to record data information, while the latter is used to record sound information, such as CD-Rs.
In the optical disks having a sector structure, an area for managing information to be recorded and a data area on which information signals are recorded by users are separated. However, when the recording system of a sector structure is applied to a multilayer recording medium, reproduced signals are distorted because of the recorded state of adjacent layers.
FIG. 9 shows a cross section of a conventional two-layer disk and an example of reproduced signals from an information layer. In the two-layer disk shown in FIG. 9(a), a first information layer 2 and a second information layer 4 are formed on a substrate 1, and a separating layer 3 is provided between the two information layers. On top of that, a protective substrate 5 is formed.
The first information layer 2 has a sector structure including a data area 8 for recording information signals and a sector address 9 spaced at predetermined intervals along the length of the data area. The sector address 9 is used for management information for recording/reproducing information signals. Similarly, the second information layer 4 also includes a data area 12 and a sector address 13.
In FIG. 9(a), the first information layer 2 is not recorded, whereas signals are recorded on the second information layer 4.
FIG. 9(b) shows reproduced signals from the second information layer 4. In this case, since transmissivity of the first information layer 2 is unchanged, constant signals in accordance with a pattern recorded on the second information layer 4 can be reproduced.
On the other hand, in FIG. 9(c), the first information layer 2 is recorded; FIG. 9(d) shows reproduced signals in such a case. Here, the first information layer 2 has the characteristic in which its transmissivity is increased by recording information. As shown in FIG. 9(d), the reproduced signals from the second information layer 4 have a waveform whose amplitude is increased in the area corresponding to the recording area of the first information layer 2.
As described above, in an optical disk having a sector structure, signals are recorded only on the data area, not on the sector address. Therefore, when information signals are reproduced, the amplitude of reproduced signals and the signal level fluctuate significantly depending on the recorded state of the opposite layer. In particular, when the reproduced signals from the second information layer are demodulated, reproduction errors are caused in the area corresponding to the boundary between the address portion and the data area of the first information layer, so that the recorded information cannot be demodulated correctly.
Similarly, in recording, the amount of light that reaches the second information layer varies depending on the recorded state of the first information layer, so that information does not recorded correctly.
The present invention is intended to solve the conventional problems described above and has an object of providing an optical information recording medium that can prevent the effect of the recorded state of other information layers and can be reproduced stably regardless of the level fluctuation of reproduced signals, a method for recording/reproducing signals on/from the optical information recording medium, and a method for manufacturing the same.
In order to achieve the above object, a first optical information recording medium of the present invention includes a substrate and at least two information layers formed on the substrate. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. A separating layer that is transparent to a wavelength of the light beams is formed between the information layers. Each information layer has a sector structure including a sector address and a data area that are divided in the circumferential direction. The positions of the sector addresses of the respective information layers coincide in the circumferential direction. The optical information recording medium described above can prevent errors during reproduction caused by the effect of other information layers, even in the case of an information recording medium of multilayer recording type with a sector structure, and thus stabilizing its recoding characteristics.
The first optical information recording medium includes a first substrate and a second substrate having a sector structure including a sector address and a data area that are divided in the circumferential direction. A first information layer is formed on the first substrate, and a second information layer opposed to the first information layer is formed on the second substrate. It is preferable that the position of the sector address of the first substrate and the position of the sector address of the second substrate coincide in the circumferential direction. The optical information recording medium described above can prevent errors during reproduction caused by the effect of other information layers, even in the case of an information recording medium of multilayer recording type with a sector structure, and thus stabilize its recording characteristics.
Furthermore, it is preferable that the amount of dislocation between the sector addresses of the respective information layers in the circumferential direction be smaller than the sum of the length of the gap between the sector address and the data area and the length of a guard data in the data area. The amount of dislocation within the above range can ensure the amplitude of reproduced signals of the data signals in the data area.
It is preferable that each information layer further includes a management area, and that a sector position identifier for identifying the position of a sector is located in the area other than the data area, the sector address, and the management area of each information layer so as to have a certain relationship to the sector address of each information layer in the circumferential direction. The optical information recording medium described above can facilitate adjusting the position of each information layer.
It is preferable that the sector position identifier is arranged in proximity to the management area at the inner circumferential region thereof, and that the shape of the sector position identifier formed on the information layer closest to the substrate is different from the shape of the sector position identifier formed on the other information layers. The optical information recording medium described above facilitates adjusting the position of each information layer further because the information layer to which the detected sector position identifier belongs can be distinguished easily.
It is preferable that each of the first and the second substrate further includes a management area, and that a sector position identifier for identifying the position of a sector is located in the area other than the data area, the sector address, and the management area of each of the first and the second substrate so as to have a certain relationship to the sector address of each of the substrates in the circumferential direction. The optical information recording medium described above can facilitate adjusting the position of each information layer.
It is preferable that the sector position identifier be arranged in proximity to the management area at the inner circumferential region thereof, and that the shape of the sector position identifier formed on the first substrate is different from the shape of the sector position identifier formed on the second substrate. The optical information recording medium described above facilitates adjusting the position of each information layer further because the information layer to which the detected sector position identifier belongs can be distinguished easily.
Next, a second optical information recording medium of the present invention includes a substrate and at least two information layers formed on the substrate. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. A separating layer that is transparent to a wavelength of the light beams is formed between the information layers. A first information layer, which is one of the information layers, has a sector structure including a sector address and a data area that are divided in the circumferential direction. The information layers other than the first information layer are provided with spiral guide grooves formed on an entire surface of a data area. The optical information recording medium described above does not require adjustment of the position of the sector address of each information layer, so that an optical information recording medium, in which the positions of the sector addresses of the respective information layers coincide in the circumferential direction, can be obtained.
In the second optical information recording medium, it is preferable that a sector address composed of a recording mark formed by irradiation of light beams be provided on the guide grooves of the information layers other than the first information layer so as to be at the same circumferential position as that of the sector address of the first information layer. The optical information recording medium described above allows the signals reproduced from the sector address of each information layer to provide equal quality. In addition, the signals of the address portion of each information layer can be reproduced with the same simple circuit.
It is preferable that the second optical information recording medium includes a first substrate having guide grooves with a sector structure including a sector address and a data area that are divided in the circumferential direction and a second substrate having spiral continuous guide grooves, and that a first information layer is formed on the first substrate and a second information layer opposed to the first information layer is formed on the second substrate. The optical information recording medium described above does not require adjustment of the position of the sector address of each information layer, so that an optical information recording medium, in which the positions of the sector addresses of the respective information layers coincide in the circumferential direction, can be obtained.
Furthermore, it is preferable that a sector address composed of a recording mark formed by irradiation of light beams is provided on the second information layer so as to be at the same circumferential position as that of the sector address of the first substrate. The optical information recording medium described above allows the signals reproduced from the sector address of each information layer to provide equal quality. In addition, the signals of the address portion of each information layer can be reproduced with the same simple circuit.
Next, a third optical information recording medium of the present invention includes a substrate and at least two information layers formed on the substrate. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. A separating layer that is transparent to a wavelength of the light beams is formed between the information layers. Each information layer is provided with a data area on guide grooves and a sector address composed of a recording mark formed by irradiation of light beams. The positions of the sector addresses of the respective information layers coincide in the circumferential direction.
Next, a fourth optical information recording medium of the present invention includes a substrate and at least two information layers formed on the substrate. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. A separating layer that is transparent to a wavelength of the light beams is formed between the information layers. Each information layer has a sector structure including a sector address and a data area that are divided in the circumferential direction. A recording mark is formed in the recording areas of all the information layers except the information layer most distant from the substrate. The optical information recording medium described above can prevent errors in a recording power suitable for the information layer from occurring.
Next, a first recording/reproducing method for an optical information recording medium of the present invention is a method for recording/reproducing information signals on/from the optical information recording medium using an optical recording/reproducing apparatus. The optical information recording medium includes a substrate, at least two information layers formed on the substrate, and a separating layer formed between the information layers. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams, and the separating layer is transparent to a wavelength of the light beams. Signals having a predetermined pattern are recorded on the recording areas of all the information layers except the information layer most distant from the substrate when the optical information recording medium is judged to be in the non-recorded state. According to the recording/reproducing method for an optical information recording medium described above, the recording of signals having a predetermined pattern can also serve for the recording to manage faults in an optical recording medium. Thus, the method is suitable for the recording of data information that requires a relatively small data capacity and a large number of files.
In the first recording/reproducing method for an optical information recording medium, it is preferable that the signals having a predetermined pattern are recorded on the information layer closest to the light beams, and then sequentially recorded on the other information layers in the order in which each information layer is positioned with respect to the light beams.
Next, a second recording/reproducing method for an optical information recording medium of the present invention is a method for recording/reproducing information signals on/from the optical information recording medium using an optical recording/reproducing apparatus. The optical information recording medium includes a substrate, at least two information layers formed on the substrate, and a separating layer formed between the information layers. The information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams, and the separating layer is transparent to a wavelength of the light beams. Information signals are recorded on the optical information recording medium in such a manner that a first information layer, which is closest to the light beams, is recorded at the beginning, and then a second information layer is recorded after the entire surface of the recording area of the first information layer has been recorded. According to the recording/reproducing method for an optical information recording medium described above, the recording of signals having a predetermined pattern can also serve for the recording to manage faults in an optical recording medium. Thus, the method is suitable for the recording of continuous signals that require a large capacity for a file, such as video signals.
In the second recording/reproducing method for an optical information recording medium, it is preferable that the information signals are recorded on the information layers sequentially in the order in which the information layers are positioned with respect to the light beams.
Next, a first method for manufacturing an optical information recording medium of the present invention includes: a first film forming step of forming a first information layer on a first substrate; a second film forming step of forming a second information layer on a second substrate; a sector position adjusting step of placing the first information layer and the second information layer opposed to each other so that a sector position of the first information layer and a sector position of the second information layer coincide, and a bonding step of bonding the first information layer and the second information layer together using at least a separating layer. The first substrate has guide grooves with a sector structure including a sector address and a data area that are divided in the circumferential direction. The first information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. The second substrate has guide grooves with a sector structure including a sector address and a data area that are divided in the circumferential direction. The second information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. The above manufacturing method can prevent errors during reproduction caused by the effect of other information layers and provide an information recording medium of multilayer recording type with a sector structure that can stabilize recording characteristics.
In the first method for manufacturing an optical information recording medium, it is preferable that the method further includes a hardening step, in which the separating layer is made of a ultraviolet curable resin, the first and the second information layer are bonded together via the layer of ultraviolet curable resin, a sector position is adjusted in the sector position adjusting step before the ultraviolet curable resin is hardened, and irradiation of ultraviolet rays for hardening the ultraviolet curable resin is performed after the adjustment of the sector position has been completed.
Furthermore, in the first method for manufacturing an optical information recording medium, it is preferable that each of the substrates further includes a sector position identifier for identifying the position of a sector, and that the sector position identifier is located in an area other than the data area, the sector address, and a management area so as to have a certain relationship to the guide grooves with a sector structure in the circumferential direction. The position of the sector position identifier is detected in the sector position adjusting step so that the amount of dislocation between the sectors of the respective information layers is adjusted based on a result of the detection. The above method can facilitate adjusting the position of each information layer.
Next, a second method for manufacturing an optical information recording medium of the present invention includes: a first film forming step of forming a first information layer on a first substrate; a sector position adjusting step of placing a stamper and the first information layer opposed to each other so that a sector position of the first information layer and a sector position of the stamper coincide; a bonding step of bonding the first information layer and the stamper together via a separating layer formed of a transparent resin layer and hardening the separating layer; a stripping step of stripping the stamper and the separating layer from the first substrate; a second film forming step of forming a second information layer on the surface of the released separating layer, and a step of protecting an information layer, in which a protective layer or a protective plate is bonded on the most distant information layer from the substrate. The first substrate has guide grooves with a sector structure including a sector address and a data area that are divided in the circumferential direction. The first information layer is formed of a thin film that shows a change that is optically detectable by irradiation of light beams. The stamper has guide grooves with a sector structure including a sector address and a data area that are divided in the circumferential direction. The above method can prevent errors during reproduction caused by the effect of other information layers and provide an information recording medium of multilayer recording type with a sector structure that can stabilize recording characteristics. Thus, the method is suitable for forming three or more information layers.
In the second method for manufacturing an optical information recording medium, it is preferable that three or more information layers are formed on a substrate by repeating the sector position adjusting step, the bonding step, the stripping step, and the second film forming step. The above method allows an arbitrary number of information layers to be laminated.
Furthermore, in the second method for manufacturing an optical information recording medium, it is preferable that the first substrate and the stamper further include a sector position identifier for identifying the position of a sector, and that the sector position identifier is located in an area other than the data area, the sector address, and a management area so as to have a certain relationship to the guide grooves with a sector structure in the circumferential direction. The position of the sector position identifier is detected in the sector position adjusting step so that the amount of dislocation between the sectors of the respective information layers is adjusted based on a result of the detection. The above method can facilitate adjusting the position of each information layer.